Interpretive Summary: Rice is an important food crop that can provide various minerals in the human diet. Because the concentrations of these minerals are low in rice, especially in milled grains, we were interested in understanding how to enhance the concentrations of minerals in rice grains. Our ultimate goal is to develop highly nutritious varieties of rice. To do this, we need new knowledge on how the plant absorbs minerals from the soil, and how it moves them to the developing grains. In this study, we grew rice plants with ample nutrients, but different levels of iron, and harvested plants at different stages of development. Harvested plants were separated into vegetative and reproductive tissues, and we measured total mineral nutrients in each part of the plant. This allowed us to determine what amounts of different minerals were coming into the plant, and how these minerals were distributed between different parts. This helped us to calculate the extent to which stored minerals in vegetative tissues, versus new uptake into the plant, were contributing to the minerals found in grains. Our results demonstrated the importance of continued root mineral absorption, during reproductive grain development, in maximizing mineral concentrations in rice grains.

Technical Abstract:
Minimal information exists on whole-plant dynamics of mineral flow through rice plants or on the source tissues responsible for mineral export to developing seeds. Understanding these phenomena in a model plant could help in the development of nutritionally enhanced crop cultivars. A whole-plant accumulation study, using harvests during reproductive development under different Fe supplies, was conducted to characterize mineral accumulation in roots, non-flag leaves, flag leaves, stems/sheaths, and panicles of Kitaake rice plants. Low Fe supply promoted higher accumulation of Zn, Cu, and Ni in roots; Mn, Ca, Mg, and K in leaves; and Zn in stem/sheaths; and a smaller accumulation of Fe, Mn, and Ca in roots and Zn and Ni in leaves. High Fe supply promoted higher accumulation of Fe in roots and Zn in leaves and a smaller accumulation of Fe in leaves and stems/sheaths and Zn, Cu, and K in roots. Correlation analyses indicated that the fluctuations in Mn-Ca, Zn-Cu, Zn-Ni, Cu-Ni, Mo-S, Ca-Mg, Cu-Mn, and Cu-Mg concentrations in response to different Fe supplies were positively correlated in leaves in at least four of the five organs analyzed. Mineral content loss analysis indicated that mineral remobilization from vegetative organs can occur in rice plants; however, for seeds to acquire minerals, vegetative remobilization is not absolutely required. Also, mineral remobilization from vegetative tissues in rice was greatly dependent of plant Fe nutrition. Remobilization was observed for several minerals from flag leaves and stems/sheaths, but the amounts were generally far below the total mineral accretion observed in panicles, suggesting that continued uptake and translocation of minerals from the roots during seed fill are probably more important than mineral remobilization.